Keratinous material, which occurs in animal hair, such as human hair consists of long polypeptide chains crosslinked to one another by means of occasional disulfide linkages. The disulfide linkages act to hold the hair in a permanent shape or configuration. Disruption of the disulfide linkages permits the polypeptide chains to function independently, allowing for the deformation of the shape of the hair without elasticity. Rupture of disulfide linkages may be accomplished by the use of various reducing agents, such as inorganic sulfides, sulfites, hydrosulfites and cyanides, mercaptans, thioglycolic acids, and various other compounds. Sulfhydryl groups are formed in place of the disulfide linkages.
In the cold-waving of hair, reduction of the disulfide linkages in hair is commonly performed in order to produce a permanent set, as in permanent waving, curling, or de-kinking of hair. The shaping of hair has conventionally been carried out by contacting the hair with a reducing agent in the form of liquids, creams, or gels while the hair has been mechanically formed into the desired new shape. The reducing composition is applied to the hair for a sufficient time to allow shaping to occur by the reductive disruption of the disulfide linkages. The reducing composition is then washed from the hair, and the normal resilience of the hair may then be regained by restoring the crosslinkages either by means of oxidizing agents or by treatment with the various crosslinking agents.
The restoration of the disulfide linkages is important in order to increase tensile strength, as well as remove the sulfhydryl groups as reactive sites. The desired crosslinking may be obtained by oxidation, as by heating in the presence of hair or by reacting with hydrogen peroxide solution. Bromates are frequently employed as oxidizing agents in the setting of permanently waved hair. Valuable properties may also be secured by the use of crosslinking agents, such as alkylene dihalides or dihalocarboxylic acids (U.S. Pat. No. 2,739,033) or dimaleimides (U.S. Pat. No. 2,850,351). By the use of crosslinking agents, it is possible to convert sulfhydryl linkages to cross linkages.
lf permanent straightening of the hair is desired, the reducing lotion is generally applied in a thickened form such as, for instance, in a cream, and evenly distributed throughout the hair by combing. The hair is combed more or less continuously and maintained in a straightened condition for a period of time sufficient to allow rupture of the disulfide linkages. The shaping agent is then washed out with water and the set is then fixed as with an oxidizing agent or a crosslinking agent.
Many of the crosslinking agents which have been proposed heretofore are not water-soluble and must be used in the form of emulsions. Some of these agents are toxic and thus difficult to employ. Others are volatile and present a hazard to people using the same.
Other crosslinking reagents not encumbered by the difficulties of past reagents is desirable.